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道,领导也。领导必需要不断呼唤,教导下属以及以身作则。下属的过和错皆因领导懒惰。

 
 
 

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Chapter 1: Production leadtime  

2012-06-24 12:54:00|  分类: Buffer Mentality |  标签: |举报 |字号 订阅

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On November 27, 2008, I went to PT Honeywell Indonesia, a subsidiary of Honeywell Avionics Singapore Inc located at Bintan Industrial Estate at Lobam, Bintan – an island in the Riau province of Indonesia. A company car fetched me from the ferry terminal to the factory that took a mere 5 minutes ride away.

I put down my laptop in my office, put on my smock and safety glasses and headed straight away to the production floor. There are 2 production lines dedicated to produce products transitioned from Deer Valley, Arizona and 11 production lines dedicated to the production of products transitioned from Olathe, Kansas. I went straight to the 11 Kansas product lines and started making a diagnosis of what are the problems hidden in these production lines.

All the Kansas lines were laid out in a similar U-shaped Group Technology cell. I went right to the end of the aisle and stopped at line #3 that was producing the KXP2290 products. At the front end of the cell are two shelves where the raw materials are stored. The next two work stations are where the final assembly of the products is carried out. Beyond the final assembly lines are the alignment station, test inspection, cold chamber temperature cycles, hot chamber temperature cycles, vibration test, burn-in chamber, box-up assembly, final test, put through the Automated Test Equipment before source inspection and finally shipped and packed for shipment to the customers.

 Figure 1-1: Process flow for KXP2290.

      A quick check with the production supervisor told me that the process cycle time for the above processes are: final assembly lines (1 hour 30 minutes) alignment station (35 minutes), test inspection (15 minutes), cold chamber temperature cycles (20 minutes), hot chamber temperature cycles (15 minutes), vibration test (45 minutes), burn-in chamber (20 hours), box-up assembly (30 minutes), final test (15 minutes) and finally put through the Automated Test Equipment (2 hours) before source inspection (15 minutes) and packed (20 minutes) for shipment of the finished goods. The sum total of the cycle time is 27 hours.

The theoretical production lead time for the production of a unit of the product is 27 hours. I asked the operations manager, Mr. Tan Woon Kit what is the production lead time used by the production planning department.

He replied, “Three days.”

Immediately I recognized the large difference between the throughput cycle time of 27 hours and his stated production lead time of 3 days is 45 hours. That is more than 1 and a half day buffer (to be exact the buffer lead time is 1 day and 21 hours).

I understand he has been using some historical data to determine the production lead time. He might have use a month’s worth of daily output data to derive the average production lead time and thereby, set it as the standard production lead time commonly across all Kansas products for all the 11 production lines. Using a standard production lead time makes it simple and easy for the production planners to remember that they must plan the loading of the production lines three days ahead of the completion of the finished goods.

Line #3 is capable to produce 5 different models of the Kansas products. Of course, the sum total of the production cycle times of all the processes for these five different models vary from one another. Some models may have to go through one or more process steps and others need one or two fewer process steps. However, using a production lead time of 3 days is more than enough to covers for the slight variation of several hours between these five products.  

I walked up to the visual display board hung from one the two shelves located at the front end of the production cell. I read the daily capacity of this cell is only 4 units. Which means for every 2 hours, a unit of product will be assembled and flowed down the entire production cell. Assuming this line operates a one 8-hour shift.

Knowing that the actual production lead time is only 27 hours, there should be 4 units of WIP residing somewhere along the production cell. However, when I read the next table below which tracks the WIP status indicated that there were more than 20 units of WIP. 9 out of the 20 units were at the E-Tech station where diagnosis and rework are being carried out. Of the remaining 11 units, there were none at the final assembly station but were scattered over the remaining test and burn-in stations.

I asked the facilitator (aka production supervisor), Rachmad why were there so many units of WIP in the line?

He replied frankly, “The shipment schedule for the units is not up yet. I have 3 days to produce them. The production lead time is 3 days.”

I asked, “Do you mean there is no urgency to complete the units and move them to the shipping department?”

“You are right. The shipping clerk won’t collect the units that are not due today. He will follow closely to the production planning schedule and comes around to collect the finished goods on their due-dates. Not a day earlier,” said Rachmad.

“But at least you can build everything all the way up to the last process as finished goods and keep them at the finished goods location pending the shipping clerk to collect them,” I put forward my point of view.

However, Rachmad replied, “The operators know when the delivery due-date is for each unit and they shall assure when the unit shall be completed in time for shipping. We do not micro-manage to this kind of exacting detail by telling the operators exactly what to do.”

I pushed my question to Rachmad: “By the way, do you think the padding of 1 day and 21 hours in the production lead time has a hand in this situation? If the production lead time is reduced to one and a half day instead of 3 days, do you think the WIP will be reduced by half?”

“Yes, definitely,” replied Rachmad, “theoretically it should be. The operators will ensure the units will move faster down the production line. But we have to give ourselves some time to buffer against quality defect, rework, and etc.”

“Do you think the one day and 21 hours is a good buffer for non-conformance in product quality, rework or any other abnormalities?” I asked.

Rachmad replied, “Historically, it is okay. We can make it to more than 90% on-time delivery provided there is no shortage of parts.”

In my mind, at such an extremely low production volume for the production cell and altogether taking less than 12 process steps, the on-time delivery should be very close to 100% and not 90%. However, ringing in my mind, things do not seem to be as easy as it was described in these few words.

I walked over to the next production cell # 5 which is a compact production line where it can produce 5 different types of products. They are: KR-87, KMA, KCM, KR 21 and KR 22. (All other production cells are designed to produce more than 5 different products up to a maximum of 12.) The red dots with a sequence number in each of them represent the production sequence for product KR-87. The blue dots represent the production sequence of KMA. You can imagine the remaining 3 products will have completely different production flows.

You notice the flow of the WIP is different for each product. It is not possible to create an ideal situation whereby the upstream station is adjacent to the down-stream station to form a physical flow of the WIP from one station to the next adjacent station. Moreover, things can get very complicate when each of the products requires totally different number of process steps ranging from 8 steps to 16 steps.

      Figure 1-2: A typical production cell #5    


Almost everyone (including both the lean production experts/masters and production managers alike) will give up trying to make this kind of multi-product production cells into a one-piece-flow production cell. It is impossible to physically layout this production line into one-piece flow for the simple reason that the line has to alternately produce several different products within the same week if not within the same day. It is not possible to re-layout the production cell every time there is a change of product in order to enable the WIP to physically flow from one station to the next station at arm length.

But the principle of one-piece-flow does not set a perquisite that the production line must be a straight or U-shape line where all the stations are placed sequentially strictly in accordance with the process sequence to produce a product. No doubt, every book on lean production or training curriculum taught in the lean expert workshops uses a simple graphic presentation where all the work stations are placed adjacent to one another in accordance with the process sequence to demonstrate what a one-piece-flow system is with an underlying assumption that the physical closeness of one station to another is a given. However, the authors of all the books on lean production and the lean masters who conducted the lean expert workshops often failed to highlight to you that there is not need to meet the physical condition of being able to actually see the WIP flowing from one station to another station laid in adjacent to one another and streamlined in the correct process sequence.

In real life, most production lines are designed to produce multiple products to maximize the efficiency of resources available and thus, are very much similar to the production cell #5 discussed above. Perhaps, a novice or non-lean expert person would like to see physical WIP moving down a production line from one station to another in quick succession.

A lean master would go for a de-coupled one-piece flow system if there are limitations that do not allow processes to be physically in adjacent to one another. All he needs is he must keep to the principle of one-piece-flow system; that is, to surface waste as and when it occurs.   

The author had many years of experiences in setting up decoupled one-piece-flow systems which often are highly complicated production cells dedicated to produce several different products. He uses an innovative “In-process Kanban system” to achieve this goal.

The “In-process Kanban system” which is dedicated to control the flow of WIP within a production cell operates differently from the material Kanban system which is used to control the flow of raw materials from the vendor or stockroom or intermediate storage on the shop floor to the production cells.

The example in Figure 3 made use of two simple concepts to set up an ‘In-process Kanban System”.

One, demarcating a location on the input end of the work-station to indicate only one unit of the WIP can be transferred to here from the upstream process. The size and shape of the Kanban location is demarcated to hold just one unit of the WIP.

Two, if a fixture or holder is required, reduce it to one fixture or holder. The example shown in the Pre-test Alignment station uses four pieces of foam to block off the four slots to reduce the WIP to only one unit. (Note: Before the lean production system was introduced, the line makes use of a buffer inventory of 5 units.)

 Figure 1-3: How an “In-process Kanban system” is implemented.

      After setting up the de-coupled one-piece-flow system using the concept of ‘In-process Kanban System”, I invited Tan Woon Kit to walk the line to review how the de-coupled one-piece-flow system works.

As we walked down the production cell #5, he nodded his head in concurrence that the line setup should work well to achieve the ideal one-piece-flow system. After all, it is not difficult for him to imagine how at every two hour interval, only a unit of product flows through the work stations.

However, he turned around and asked me this question. He said, “Before I agree to reduce the production lead time to 1 and ? days, you must assure me that the operators understand exactly how this de-coupled one-piece-flow system works.”

I replied, “Please be assured that this “In-process Kanban System” is very simple and all your operators shall comply with easily. If any one of the operators does not understand how this system works and violates the Kanban rules, I have failed you. After all, one of the key philosophies behind the Toyota Production System is ‘Simple’.”

I went on to explain an instruction card placed at the work-stations. It is called an In-process Kanban card. Figure 4 below shows exactly the Kanban instructions used for a typical[1] process/work station which is neither the first nor last process/work station. 

When the “In Kanban” is ‘0’, the operator at this station will have to do either or both of these two things. One, he has to check with the upstream process/work station when the next unit of WIP will be delivered to him. Two, he has to inform his facilitator (aka production supervisor) that he has run out of WIP and hence will be idle. If the “In-Kanban” is equal to one unit, he merely concentrates to process the current unit on-hand.

After he had completed the unit on-hand, he looks out for whether his “Out Kanban” is equal to ‘1’ or ‘0’. If the quantity at the “Out-Kanban” is ‘0’, he will place his recently completed unit onto the “Out Kanban” location and gets back to his station to begin processing the next unit. If the “Out Kanban” has a quantity of ‘1’ unit of WIP, he must stop immediately and keep the recently completed unit at his work station. This will prevents the piling up of WIP more than the designated quantity of one piece at the Kanban location of the down-stream process/work station.  

 Figure 1-4: A typical Kanban instruction card

      The most beautiful thing about this one-piece-flow system is that every single unit of product that passed through the production cell does not spend much time sitting as WIP in-between two processes/work stations. Without the piling of WIP to more than one unit, the total time taken by a unit of product is slightly more than the sum of the cycle time of all the processes that the unit passed through. This guarantees the production lead time is the shortest.

Summing up, it is easy to find fault that the operations manager is padding his production lead time and that leads to the build up of WIP in the production floor unnecessarily. However, unless you can design a one-piece-flow production system, you are not able to convince him to get rid of his buffer mentality.  



[1] The Kanban instruction card for the first station and the last station and possibly for some other stations may not be exactly the same as the one shown here. The Kanban quantity may not be equal to 1 unit.

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